Selective hydrotreating of different hydrocarbonaceous feedstocks in temperature regulated hydrotreating zones

ABSTRACT

IN THE SELECTIVE HYDROTREATMENT OF ANY PLURALITY OF DIFFERENTLY CONSTITUTED HYDROCARBONACEOUS FEEDSTOCKS IN A PLURALITY OF HYDROTREATING ZONES, WHEREIN A FIRST SUCH FEEDSTOCK IS HYDROTREATED IN ADMIXTURE WITH AN EXCESS OF HYDROGEN IN A FIRST HYDROTREATING ZONE TO OBTAIN A FIRST ZONE EFFLUENT THAT IS THEN FED TO A SECOND HYDROTREATING ZONE INT WHICH A SECOND HYDROCARBONACEOUS FEEDSTOCK IS INTRODUCED, THE FIRST ZONE EFFLUENT IS COOLED TO A TTEMPERATURE WITHIN A PREDETERMINED RANGE PRIOR TO HYDROTREATMENT IN THE SECOND ZONE, THE SECOND FEEDSTOCK CONSTITUTING A PARTIAL BUT NOT THE SOLE COOLANT FOR THE COOLING. SUPPLEMENTAL COOLING IS PROVIDED DIRECTLY BY CONTACT WIT INJECTED WATER OR INDIRECTLY BY INTERSTAGE COOLING EXTERIORLY OF THE HYDROTREATING ZONES.

April 17, 1973 J, ANTEZANA ETAL 3,728,249

SELECTIVE HYDROTREATING DIFFERENT HYDROCARBONACEOUS FEEDSTOCKS IN TEMPERATURE REGULATED HYDROTREATING ZONES Filed Feb. 5, 1971 FURNACE HYDROCENATION REACTOR -|8u FIG- I- PRODUCT TO 34 RECOVERY 1 HYDROCENATION Hg REACTOR- TREAT @7 I08 Ill H27 x Q COOLANT INVENTORS FERNANDO J. ANTEZANA, PRODUCT JACK M.HOCHMAN, TORECOVERY HAROLD N. EINBERC,

United States Patent U.S. Cl. 208-57 Claims ABSTRACT OF THE DISCLOSURE In the selective hydrotreatment of any plurality of differently constituted hydrocarbonaceous feedstocks in a plurality of hydrotreating zones, wherein a first such feedstock is hydrotreated in admixture with an excess of hydrogen in a first hydrotreating zone to obtain a first zone effluent that is then fed to a second hydrotreating zone into which a second hydrocarbonaceous feedstock is introduced, the first zone effluent is cooled to a temperature within a predetermined range prior to hydrotreatment in the second zone, the second feedstock constituting a partial but not the sole coolant for the cooling. Supplemental cooling is provided directly by contact with injected water or indirectly by interstage cooling exteriorly of the hydrotreating zones.

BACKGROUND OF THE INVENTION Field of the invention This invention is directed to the simultaneous hydrogenation or hydrofining hydrotreatments in a single reactor of a plurality of hydrocarbonaceous feedstocks of different compositions, such feedstocks suitably being derived from petroleum crude oils, shale oils, tar sand oils, liquefied coal products, and the like. More particularly, it relates to the cooling of the effiuent from a first hydrotreatlng zone in which a first such hydrocarbonaceous feedstock is reacted with hydrogen under hydrotreating conditions, the cooling being effected either by direct contact with injected water or indirectly through an interstage heat exchanger, so that the efiiuent from the first hydrotreating zone has a temperature within a predetermined range before being introduced into a second hydrotreating zone for hydrotreatment in admixture with a second hydrocarbonaceous feedstock of different composition from the first such feedstock.

Prior processes In producing fuel products either from petroleum, coal, shale, or tar sand sources, various hydrocarbonaceous streams differing in hydrogen-deficiencies, boiling points, and sulfur and nitrogen contents are developed at diverse stages in processing. These are streams which must be hydrotreated to upgrade hydrogen content and/ or to hydrodenitrogenate and hydrodesulfnrize them, either to produce satisfactory product, on the one hand, or streams suitable for further processing or other use, on the other hand. Heretofore, hydrotreating of different hydrocarbonaceous streams was accomplished by combining one or more streams into a single stream and nonselectively hydrotreating that stream in a single reactor, or else by individually hydrotreating uncombined streams in reactors either dedicated to them or blocked to process only one stream at a time. In an application for US. Letters Patent, Ser. No. 112,938, by Jack M. Hockrnan and Harold N. Weinberg, entitled Selective Simultaneous Hydrotreating of Different Hydrocarbonaceous Feedstocks in a Single Reactor, filed Feb. 5, 1971 and assigned to the assignee of the present application, a new process for selec tively hydrotreating of a plurality of hydrocarbonaceous feedstocks of different compositions is disclosed. According to the process, a first hydrocarbonaceous feedstock is hydrotreated in a first hydrotreating zone in admixture with an excess of hydrogen to obtain a first zone effluent. The first zone effiuent is then hydrotreated in a second hydrotreating zone in admixture with a second hydrocarbonaceous feedstock, the second hydrocarbonaceous feedstock being of different composition from the first feedstock. The hydrogen uptake of the first feedstock is greater, and the hydrogen uptake of the second feedstock is lesser, than if the first and second feedstocks had been hydrotreated together in both the first and second hydrotreating zones. The feed rates of the first and second feedstocks and the hydrotreating conditions in the first and second hydrotreating zones are correlated to effect a predetermined hydrogen uptake by the first feedstock in the first and second hydrotreated zones and to effect a predetermined hydrogen uptake by the second feedstock in the second hydrotreating zone. In addition, the second feedstock is introduced into the second hydrotreating zone at a feed rate and at a temperature sufficient to reduce the temperature in the second hydrotreating Zone. In some instances, the temperature and feed rate of the second feedstock can be correlated with the feed rate of the first feedstock not only to provide desired hydrogen uptakes, but also to provide sufiicient quench of the heat in the first zone effluent to reduce the temperature in the sec ond hydrotreating zone at a desired level. In other cases, supplemental cooling of the first zone effluent is needed in order to reduce the temperature in the second hydrotreating zone to within a predetermined range. Heretm fore, cooling of hydrotreating zones has primarily involved high rates of cold recycle treat gas. The present invention is directed to less costly means of supplementing the quench provided to the second hydrotreating zone by the second feedstock of the referenced application for Letters Patent. An unexpected benefit of one means of providing this supplemental quench is an increased hydrotreating activity in the second hydrotreating zone.

Prior patents considered in the preparation of this application include US. Pats. 2,303,075; 2,689,821; 2,707,- 163; 2,796,386; 2,971,901; 2,901,423; 3,015,619; 3,147. 210; 3,248,316, 3,441,626; and 3,471,582.

SUMMARY OF THE INVENTION In accordance with this invention, a first hydrocarbonaceous feedstock is hydrotreated in a first hydrotreating zone in admixture with an excess of hydrogen to obtain a first zone efiiuent. The first zone efiluent is then hydrotreated in a second hydrotreating zone in admixture with a second hydrocarbonaceous feedstock, the second hydrocarbonaceous feedstock having a composition different from the first hydrocarbonaceous feedstock. The first and second feedstocks are introduced, respectively, into the first and second hydrotreating zones, at feed rates correlated for the hydrotreating conditions in such zones to effect a predetermined hydrogen uptake by the first feedstock in the first and second zones and by the second feedstock in the second zone. Prior to hydrotreating the admixture of the first zone effiuent and the second feedstock in the second hydrotreating zone, however, the first zone effiuent is cooled to a temperature within a predetermined range, the second hydrocarbonaceous feedstock constituting a partial but not the sole coolant for the cooling at its rate of introduction to the second hydrotreating zone. In one form of the invention, the cooling of the first zone efiluent to a desired temperature is partially effected by indirectly cooling the first zone effluent exteriorly of said hydrotreating zones before admixing the second hydrocarbonaceous feedstock with the effiuent. In

another form of the invention, the second hydrocarbonaceous feedstock and water are introduced into a second hydrotreating zone at a location downstream from the first hydrotreating zone to admix with the first zone effluent, the quantity and temperature of the water being correlated with the quantity and temperature of the second feedstock and the temperature at that location so as to cool the second hydrotreating zone to a temperature within a predetermined range. Preferably, in either form, the second feedstock and the supplemental coolant together quench an amount of heat in the first zone efiluent substantially equal to that generated by the hydrotreating reactions in the first hydrotreating zone.

Hydrotreating conditions in the first and second zones suitably include a temperature within the range from about 650 F. to about 850 F., a pressure within the range from about 680 p.s.i.g. to about 2000 p.s.i.g., an overall liquid hourly space velocity within the range from about 0.2 w./hr./w. to about 2.0 w./hr./w., and a hydrogen treat rate within the range from about 1000 to about 10,000 s.c.p. per barrel of total feed. In the hydrotreating processes, the first feedstock will normally have a greater hydrogen deficiency, will boil over a range of temperatures at least partially higher, will have a greater reducible sulfur content, or will have a greater organic nitrogen content, or some combination thereof, than the second feedstock will have.

The hydrotreating catalysts employed are of conventional nature. Without being limited to any particular catalyst, these catalysts will typically comprise an alumina or silica-alumina support carrying one or more iron group metals and one or more metals of Group VI-B of the Periodic Table in the form of the oxides or sulfides. In particular, combination of one or more Group VI B metal oxides of sulfides with one or more Group VIII metal oxides or sulfides are preferred. For example, typical catalyst metal combinations contemplated are oxides and/ or sulfides of cobalt-molybdenum, nickel-tungsten, nickelmolybdenum-tungsten, cobalt-nickel-molybdenum, nickelmolybdenum, etc. As a typical example, one catalyst will comprise a high metal-content sulfided cobalt-molybdenum, alumina catalyst containing about 1 to 10 weight percent cobalt oxide and about to 40 weight percent molybdenum oxide, especially about 2 to 5 weight percent cobalt and about to 30 weight percent molybdenum. It will be understood that other oxides and sulfides will be useful, such as those of iron, nickel, chromium, tungsten, etc. The preparation of these catalysts is now well known in the art. The active metals can be added to the relatively inert carrier by impregnation from aqueous solutions followed by drying and calcining to activate the composition. Suitable carriers include, for example, activated alumina, activated alumina-silica, zirconia, titania, etc., and mixtures thereof. Activated clays, such as bauxite, bentonite and montmorillonite, may also be employed.

In supplementing the quench of the first hydrotreating zone effluent in accordance with this invention, either the indirect heat exchange of the first zone efiiuent with a coolant in an interstage cooling zone, or the direct cooling of the efliuent by contact with water, are less costly than a hydrogen treat gas recycle system, in eliminating recycle compressor units and in reducing the sizes of feed preheat furnaces and effluent heat exchangers associated with such recycle systems.

As supplemental quench, water, which vaporizes to steam, has several other advantages. It improves catalyst activity and permits a reduced catalyst volume, if desired. Also, by varying the water feed rate at any quench point, an additional degree of freedom is provided in tailoring the hydrotreating of any feedstock. The beneficial effect of water as supplemental quench is illustrated by improvements obtained in hydrosulfurization of a Tia Juana medium atmospheric residuum over a cobalt molybdate catalyst on an alumina base (12.5% molybdenum trioxide, 3.5% cobalt oxide, 1.8% silicon dioxide, and about 82% alumina) under hydrotreating conditions including a temperature of 650 F., a pressure of 1500 p.s.1.g. and a hydrogen treat rate of 1500 s.c.f./b. (96% H During the first 5 8 days of the run, no steam was added to the hydrogen, during which time the second order activlty rate of the hydrodesulfurization hydrotreatment declined at a constant expected rate. At day 59, 10 volume percent of steam was added with the hydrogen feed, and unexpectedly produced an increase of about 35% in activity. On mcreasing the steam addition rate to 20 volume percent at day 71, an additional 30% increase in activity was obtained. However, for the increased activity, the rate of catalyst deactivation was not significantly different than before steam was added.

A detailed description of specific preferred embodiments of the invention, as depicted in the drawings, will further illustrate the invention.

DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic flow diagram of a system for selectively hydrotreating a plurality of hydrocarbonaceous feedstocks in a plurality of hydrotreating zones WhlCh uses water with part of the feedstock feed to serve as heat quench of the efiluent from a first hydrotreating zone; and

FIG. 2 is a schematic fiow diagram of a hydrotreatlng system like that of FIG. 1, except that interbed cooling is used to supplement the cooling of the first hydrotreating zone efiinent provided by a second hydrocarbonaceous feedstock.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG. 1, a first hydrocarbonaceous feedstock in line 10 is combined with an excess of a hydrogen treat gas needed for hydrotreating, introduced by way of line 12, and the combined streams are indirectly heated in a furnace 14 for introduction by way of line 16 into hydrotreating reactor 18 at a predetermined temperature. The feedstock from line 10 and the hydrogen are then passed in admixture through a first hydrotreating zone 18a in contact with a hydrotreating catalyst under hydrotreating conditions to obtain a first zone effluent. A second hydrocarbonaceous feedstock of different composition from the feedstock of line 10 is introduced by way of line 20 (valve 21 open) into hydrotreating reactor 18 to admix with the efiluent from zone 18a. The admixed first and second feedstocks then pass through the second hydrotreating zone 18b in contact with a suitable hydrotreating catalyst under suitable hydrotreating conditions to produce a second zone effluent. In the same manner, a third hydrocarbonaceous feedstock is introduced by way of line 22 (valve 23 open) into hydrotreating reactor 18 between second hydrotreating zone 18b and third hydrotreating zone to admix with the effiuent from zone 18b, the admixture thereafter passing into zone 180 to contact a hydrotreating catalyst under hydrotreating conditions to produce a third zone effluent. Likewise, a fourth hydrocarbonaceous feedstock is introduced by way of line 24 (valve 25 open) into hydrotreating reactor 18 between third hydrotreating zone 18c and fourth hydrotreating zone 18:1 to admix with the third zone efiiuent, the admixture then flowing downwardly through the fourth hydrotreating zone 18d for contact with a hydrotreating catalyst therein under hydrotreating conditions to produce an effluent which is subsequently removed from the reactor by way of line 34 for product recovery. At least one of first, second, third, and fourth feedstocks is of different composition than the other such feedstocks.

In accordance with this invention, the feed rates of the hydrocarbonaceous feedstocks introduced into the hydrotreating reactor by way of lines 16, 20, 22, and 24 are correlated with the hydrotreating conditions in the hydrotreating zones 18a-18d to effect a predetermined hydrogen uptake by each such feedstock, and water is introduced with the second and/or third and/or fourth feedstock, as needed, to provide additional quench for the first zone effluent, and/or second zone effluent, and/ or third zone efiluent, when the quantity and temperature of second, third, or fourth feedstock is insufficient in and of itself to reduce the temperature, respectively, of the first zone effluent, second zone effluent, or third zone effluent, to within a predetermined range. Thus, water is selectively introduced from line 26 into one or more of feedstock lines 20, 22, and 24, as needed, by way of branch lines 28, 30, and 32 on appropriate opening or closure of valves 29, 31, and 33. For example, additional water quench may be needed only for the second zone effluent and the third zone efliuent in a case where the quantity and temperature of the second feedstock is alone suflicient to reduce the temperature of the first zone efiluent to a level desired for hydrotreating zone 18b, the quantity and temperature of the third and fourth feedstocks each being inadequate, however, to reduce the temperatures, respectively, of the second and third zone effluents, to an extent desired. In this case, valve 33 is closed and water from line 26 is metered only into lines 22 and 24 by way of branch lines 28 (valve 29 open) and 30 (valve 31 open). The amount of water needed in line 22 and 24 is adjusted by manipulation of valves 29 and 31 and adjustment of flow rate from line 26. The temperature of the water is correlated with its quantity and the temperature of the second and third zone effiuents with which it is mixed, as well as with the quantity and temperature of the third and fourth feedstocks it is introduced with, so as to reduce the temperature of the second and third zone efiluents to within a range predetermined as needed, respectively, for zones 18c and 18d. The amount of water introduced by way of lines 28 and 30 is also correlated with the increased hydrotreating activity effected in zones 18c and 18d thereby to provide the hydrogen uptake desired for the feedstocks flowing through zones 18c and 18d.

Indirect supplemental quench is illustrated in FIG. 2. Referring to FIG. 2, a first hydrocarbonaceous feedstock in line 100 is combined with an excess of hydrogen treat gas in line 102, as needed for hydrotreating in hydrotreating reactor 108, and the combined streams are heated in furnace 104 for introduction by way of line 106 into hydrotreating reactor 108. The combined first feedstock and hydrogen gas are passed in admixture through a first hydrotreating zone 108a in contact with a suitable hydrotreating catalyst under suitable hydrotreating conditions to obtain a first zone eflluent. In a case where the effluent from the first zone 108a will not be cooled to a desired level for zone 108b by the quantity and temperature at which a second feedstock is introduced into second hydrotreating zone 108b for a predetermined hydrotreating, the total first zone efiluent is withdrawn from first hydrotreating zone 108a by way of line 130 (valve 131 open) and indirectly cooled exteriorly of hydrotreating reactor 108 in an external tube in shell or other suitable heat exchanger 128. The cooled first zone efiluent is then returned by way of line 132 to hydrotreating reactor 108 between first hydrotreating zone 108a and second hydrotreating zone 108b for admixture therewith the second hydrocarbonaceous feedstock introduced thereinto by way of line 110 (valve 111 open). The extent to which the temperature of the first zone effluent is reduced in heat exchanger 128 is correlated with the quantity and temperature of the second hydrocarbonaceous feedstock introduced by way of line 110 so that, after mixing with the second feedstock, the first zone effluent is reduced to a temperature desired for hydrotreating zone 108b. In the same manner, where a third hydrocarbonaceous feedstock (introduced into reactor 108 between second and third hydrotreating zones 108b and 1080 by line 112, valve 113 open) or a fourth such feedstock (introduced between third and fourth hydrotreating zones 108a and 108d, by means of line 114, valve 115 open) are insufficient in quantity and temperature to reduce the temperature, respectively, of the effluent from the third or fourth hydrotreating zones 1080 and 108d, the efiluent from such zone (or zones) is withdrawn for coordinated cooling in external heat exchangers. Thus, if necessary, valve is opened and the second zone etlluent is withdrawn for cooling in heat exchanger 126 and returned by line 136 to between zones 108b and 1080 for admixture with the second feedstock, introduced by line 112, the combined quench of the external heat exchanger 126 and the second feedstock reducing the temperature of the second zone efiluent to within a predetermined range desired for third hydrotreating zone 108c. Similarly, if needed, the fourth zone effluent is withdrawn by line 138 (valve 139 open), cooled to a temperature within a predetermined range in heat exchanger 124, and returned by line to admix with the fourth feedstock, introduced by line 114 (valve 115 open), the combined coolants reducing the temperature of the third zone effluent to a lower temperature within such predetermined range, as desired for hydrotreating in fourth hydrotreating zone 108d. Coolant is supplied to heat exchangers 124, 126, and 128 through trunk lines from main line 116. Trunk line 118 (valve 117 open) supplies coolant to heat exchanger 124, line 125 withdrawing the heated coolant. With valve 119 open, coolant is circulated through heat exchanger 126 by lines 120 and 129 (valve 121 open), and through heat exchanger 128 by lines 122 and 127 (valve 123 open). Hydrotreated product is withdrawn by line for recovery.

EXAMPLES The hydrotreating process on which the cooling aspects of this invention are premised will be illustrated by Example I, which compares hydrotreating by earlier single pass methods to the subject process.

EXAMPLE I (A) Conventional case: Single pass hydrogenation A coal liquid boiling over the range from about 400 F. to about 700 F. and having a hydrogen content of 8.84 wt. percent is fed at the rate of 100 lbs. per hour to the inlet of a hydrogenation reactor where it is hydrogenated in the presence of a cobalt molybdate catalyst (l-lO wt. percent cobalt oxide and 5-40 wt. percent molybdenum oxide) on an alumina support under hydrogenation conditions including a temperature of about 700 F., a pressure of about 1300 p.s.i.g., a hydrogen treat rate of about 5000 s.c.f./h. of total feed and a liquid hourly space velocity of about 1.0 w./hr./wt. Total hydrogen uptake is 800 s.c.f./b. of total feed. Exothermic heat generated by the hydrogenation reaction is controlled by cold treat gas recycle. The eifiuent recovered from the hydrogenation reactor has a hydrogen content of 9.96 wt. percent. On fractionation with a cut point of 530 F., with 400-530 P. fraction has 9.37 wt. percent hydrogen and 530-700 F. fraction has a hydrogen content of 10.68 wt. percent.

(3) Split feed quench cases 'In one case, a heavy 530/700 F. coal liquid cut having a hydrogen content of 8.29 wt. percent is fed to the reactor inlet (top). The hydrogenation reactor is operated under conditions like those in the single pass hydrogenation case, and a light 400/530" F. coal liquid fraction having a hydrogen content of 9.45 wt. percent is fed to the reactor as quench after 50% of the total required hydrogen uptake of 800 s.c.f./b. has occurred. In a variation of case one, the light out is fed to the top of the reactor and the heavy cut used as quench.

In a second case, the heavy and light coal liquid fractions are fed to the reactor as in case one and its variation, except that the feed used as quench is fed to the reactor at the point where 25% of the required 800 s.c.f./b. H uptake/B of total feed occurs.

Based on experimental rate equations for the total feed, the light cut alone and the heavy cut alone, the following results occur:

SELECTIVE DISTRIBUTION OF HYDROGEN UPTAKE IN LIQUID PRODUCT Case 1 Case 2 Conventional 4 case, total Heavy Light Heavy Light feed at top at top at top at top at top Heavy cut, wt.

percent H2.-. 9. 37 9.63 9.13 9. 48 9. 27 Light cut, wt.

percent Hz.-. 10. 68 10. 33 10. 90 10. 53 10. 76

A plurality of coal liquefaction streams from a coker scrubber, a coker fractionator and a cat cracker fractionator are hydrogenated before being fed to a cat cracker reaction zone, in order to minimize the formation of coke in the cake cracking zone. A 700 F.+ stream from a coker scrubber which has a hydrogen content of 6.66 weight percent is combined with about 7000 s.c.f./b. of hydrogen treat gas and heated in a furnace to 653 F., after which it is introduced at the rate of 66,100 barrels per day into the inlet of a hydrogenation reactor comprising four hydrogenation zones each containing a bed of cobalt molybdate catalyst. The beds can vary in size, but suitably the first three zones contain beds of about 13,000 cubic feet, while the last zone has a 36,000 cubic feet bed. The beds in the hydrogenation reactor are maintained at a temperature of about 700 F. under a pressure of 1800 p.s.i.g. A cat cracker recycle bottoms stream boiling above 650 F. having a hydrogen content of 6.40 weight percent is introduced into the hydrogenation unit between the first and second hydrogenation zones, at a temperature of about 512 F. and at a daily rate of 31,400 barrels. The coker fractionator stream, boiling over the range from 550 F. to 700 F. and having a hydrogen content of 7.76 weight percent is introduced between the second and third hydrogenation zones at a rate of 41,950 barrels per day and a tem perature of 517 F. Finally, a cat cracker recycle stream boiling over the range from about 450 to about 650 F. and having 8.60 weight percent hydrogen is introduced at a temperature of 449 F. into the hydrogenation unit between the third and fourth hydrogenation zones at a rate of 79,000 barrels per day. The effiuent from each hydrogenation zone flows into the next downstream zone in admixture with the stream introduced between each zone. Quench water is added with each of the cat cracker recycle bottoms stream, the coker fractionator stream, and the cat cracker recycle stream, at a total feed rate of 870 gallons per minute and a mean temperature of 110 F. The liquid hourly space velocity of the coker scrubber stream is lowest, about 0.5 w./hr./w., and that of the hydrocracker fractionator side stream is highest, about 2.0, and the coker fractionator stream is intermediate, from about 0.8 to about 1.2 or so. The hydrogen content of the product stream recovered from the hydrogenation reactor is 9.5 weight percent.

Having now fully described our invention in several embodiments and examples, various modifications and changes for accomplishing the same ends by substantially similar means will occur to those in the art; however, insofar as such modifications and changes are within the spirit and scope of the appended claims, they are deemed part of the invention.

We claim:

1. A process for selectively hydrotreating a plurality of hydrocarbonaceous feedstocks in a plurality of hydrotreating zones, which comprises:

in a first hydrotreating zone, hydrotreating a first such feedstock in admixture with an excess of hydrogen, to obtain a first zone efiluent,

in a second hydrotreating zone, hydrotreating said first zone effluent in admixture with a second such feedstock, said second feedstock having a composition different from said first feedstock,

whereby the hydrogen uptake of said first feedstock is greater, and the hydrogen uptake of said second feedestock is lesser than if said first and second feedstocks had been hydrotreated together in both said first and second hydrotreating zones, and

prior to hydrotreating said admixture in said second hydrotreating zone, cooling said first zone efliuent to a temperature within a predetermined range, said second feedstock contributing partially toward said cooling.

2. A process for selectively hydrotreating a plurality of hydrocarbonaceous feedstocks in a plurality of hydrotreating zones which comprises:

introducing a first such feedstock and an excess of hydrogen into a first hydrotreating zone, to obtain a first zone efliuent,

introducing a second such feedstock of different composition from said first feedstock into a second hydrotreating zone to admix with said first effiuent, prior to introducing said second feedstock indirectly cooling said first zone effluent to a temperature within a predetermined range exteriorly of said first and second hydrotreating zones in a cooling zone tthrough which a coolant is circulated, the quantity and temperature of said second feedstock being correlated with said temperature of said cooled first zone effluent so as to cool said second hydrotreating zone to a lower temperature within said predetermined range, whereby the hydrogen uptake of said first feedstock is greater, and the hydrogen uptake of said second feedstock is lesser, than if said first and second feedstocks had been hydrotreated together in both said first and second hydrotreating zones. 3. A process for selectively hydrotreating a plurality of hydrocarbonaceous feedstocks in a plurality of hydrotreating zones, which comprises:

introducing a first such feedstock and an excess of hydrogen into a first hydrotreating zone, to obtain a first zone efiluent,

introducing a second such feedstock of different composition from said first feedstock and water into a second hydrotreating zone at a location downstream from said first hydrotreating zone to admix with said first zone effluent,

the quantities and temperature of said second feedstock and said water being correlated with the temperature at said location so as to cool the second hydrotreating zone to a temperature within a predetermined range,

whereby the hydrogen uptake of said first feedstock is greater, and the hydrogen uptake of said second feedstock is lesser than if said first and second feedstocks had been hydrotreated together in both said first and second hydrotreating zones.

4. A process for selectively hydrotreating a plurality of hydrocarbonaceous feedstocks in a plurality of hydrotreating zones in a hydrotreating unit, which comprises:

introducing a first such feedstock and an excess of hydrogen at predetermined feed rates into the inlet of a first hydrotreating zone and passing them in admixture therethrough in contact with a hydrotreating catalyst under hydrotreating conditions to obtain a first zone efiluent,

introducing a second such feedstock of different composition from said first feedstock and water into said hydrotreating unit between said first hydrotreating zone and a second hydrotreating zone to adrnix with said first zone efliuent, said second feedstock and said water being introduced at a feed rate and at a temperature suflicient to reduce the temperature of said first zone effluent to with a predetermined range,

passing said first zone effluent and said second feedstock in admixture through a second hydrotreating zone in contact with a hydrotreating catalyst under hydrotreating conditions, the feed rates of said first and second feedstocks and the hydrotreating conditions in said first and second hydrotreating zones being correlated to effect a predetermined hydrogen uptake by said first feedstock in said first and second hydrotreating zones and to effect a predetermined hydrogen uptake by said second feedstock in said second zone,

whereby the hydrogen uptake of said first feedstock is greater, and that of said second feedstock is lesser than if said first and second feedstock had been introduced together into said inlet and passed in admixture through said first and second hydrotreating zones.

5. The process of claim 4 in which said second feedstock and said water is introduced into said second bydrotreating zone in an amount and at a temperature calculated to quench an amount of heat in said first zone effluent substantially equal to that generated by the hydrotreating reactions in said first hydrotreating zone.

6. The process of claim 4 in which said first feedstock has a greater hydrogen deficiency than said second feedstock.

7. The process of claim 4 in which said first feedstock boils over a range of temperatures at least partially higher than the range of temperatures over which said second feedstock boils.

8. The process of claim 4 in which said first feedstock has a greater reducible sulfur content than said second feedstock.

9. The process of claim 4 in which said first feedstock has a greater organic nitrogen content than said second feedstock.

10. The process of claim 4 wherein the hydrotreating conditions in said first and second hydrotreating zones include:

a temperature within the range from about 650 F. to

about 850 F.

a pressure within the range from about 680 p.s.i.g. to

about 2000 p.s.i.g.,

an overall liquid hourly space velocity within the range from about 0.2 w./hr./w. to about 2.0 w./hr./w., and

a hydrogen treat rate within the range from about 1000 to about 10,000 s.c.f. per barrel of total feed.

References Cited UNITED STATES PATENTS 3,592,759 7/1971 Pollitzer 208-89 3,171,862 3/1965 Larkins et a1 260672 2,971,901 2/ 1961 Halik et al 208-59 2,878,179 3/1959 Hennig 208-210 3,617,526 11/ 1971 Coons et a1 208-210 DELBERT E. GANTZ, Primary Examiner G. E. SCHMITKONS, Assistant Examiner U.S. Cl. X.R. 20858, 59, 143, 210 

